The present invention relates to a process for producing an insulating layer buried in a semiconductor substrate by ion implantation. It more particularly applies to the field of producing MOS integrated circuits of the silicon on insulant type.
Silicon on insulant technology (SOI) provides a significant improvement compared with standard methods in which the active components of the integrated circuits are produced directly on a solid monocrystalline silicon substrate. The use of an insulating support leads to a marked reduction in the stray capacitances between the source and the substrate on the one hand and the drain and the substrate on the other of the active components of the circuits and consequently to an increase in the operating speed of said circuits. It also leads to a great simplification in the production processes, to an increase in the integration density, to an improved behaviour of the circuits at high voltages and to a limited sensitivity to radiation as a result of the small monocrystalline silicon volume. This technology also makes it possible to obtain monocrystalline silicon islands, which are isolated from one another and in which can be formed the different components of an integrated circuit.
One of the presently known SOI technologies is the silicon on sapphire or SOS technology, in which the components are produced in a thin silicon film epitaxied on a sapphire insulating substrate. This technology suffers from several disadvantages and in particular the cost of the sapphire substrate is high and the epitaxy of the thin silicon film on the substrate is difficult. In addition, the thin silicon film has a large number of defects due to its production process.
Other technologies have been investigated in order to obviate these disadvantages. Among these reference can be made to those involving the recrystallization of an amorphous or polycrystalline silicon film deposited on an amorphous substrate, such as of silicon oxide. The silicon is recrystallized by using lamps, lasers or heating elements making it possible to supply the heat necessary for melting the amorphous or polycrystalline silicon. Unfortunately said technology suffers from disadvantages linked more particularly with the poor quality of the silicon--insulant interface (e.g. parasitic channel at the interface).
Other technologies based on the a posteriori production of the insulating material, i.e. on the basis of solid monocrystalline silicon have been envisaged. Reference is e.g. made to the process of implanting high dose nitrogen or oxygen ions in solid monocrystalline silicon making it possible to form, following high temperature annealing of the substrate, a buried insulating silicon oxide or silicon nitride film. This process known as separation by Implanted Oxygen or SIMOX is in particular described in the article by P. L. F. Hemment et al in Nuclear Instruments and Methods 209/210, 1983, pp 157-164 entitled "Formation of buried insulating layers in silicon by the implantation of high doses of oxygen."
However, in this SIMOX process, the passage of the nitrogen or oxygen ions to a greater or lesser extent damages the monocrystalline silicon film surmounting the insulating layer and particularly in the regions of said silicon film in which will be formed the active zones of the active components of the integrated circuits. The defects produced are prejudicial to the obtaining of a satisfactory operation of the components.